Acute Megakaryoblastic Leukemia is characterized by the blocked differentiation and improper proliferation of megakaryocytes. The 1;22 chromosomal translocation that has been found to associate with AMKL infants implicates the fusion gene product in leukemiogenesis. The fusion gene consists of full length MKL1 fused in frame and downstream of RBM15. Our lab focuses on the normal and aberrant functioning of MKL1, a myocardin related transcription factor, in the regulation of megakaryocytopoiesis. We propose to study MKL1 in murine embryonic stem (ES) cells in an attempt to mimic developmental hematopoiesis and further understand the disease in the neonatal system. We will test if enforced and misexpression of MKL1 has an effect on megakaryocyte differentiation. To test the hypothesis that enforced expression of MKL1 promotes mouse ES cell differentiation we will develop an inducible MKL1 ES cell line and analyze it for MK differentiation. In addition, we will conduct studies to determine the requirement for MKL1 and/or MKL2 in megakaryocyte differentiation. To do this, we will construct inducible ES cell clones expressing a dominant negative MKL1 or shRNA against MKL1 and/or MKL2. To determine the effects on megakaryocytopoiesis we will use CFU-Mk (a functional assay), flow cytometric analysis (a phenotypic assay), and cytospin preparations (a morphological assay). Concurrent with the cell culture investigations, we will conduct a more hematopoietic focused analysis of MKL1-/- mice and further manipulate the animal model to discern the role of MKL1 in megakaryocytopoiesis. The goal of the work is to create a mouse system that can be translated into human cells for the study of AMKL caused by the 1;22 translocation. This transition will create opportunities for therapy based research and ultimately more informed and precise treatments for afflicted individuals.